The present invention relates to a velocity control device and method for a magnetic disc apparatus so as to allow a magnetic head to seek a target track.
Recently, in a conventional compact magnetic disc apparatus, one side of the magnetic disc is entirely used for storing not only servo data of magnetic head positioning. As shown in FIG. 1, data sectors 2 and servo sectors 3 for storing servo data may be intermixed in a data area of a magnetic disc 1. The magnetic disc apparatus of this type allows effective utilization of the data area on the magnetic disc.
However, in a magnetic disc apparatus having no special servo data area as described above, position data of the magnetic head is not always obtained. In fact, the position data is obtained only from the servo sectors 3 shown in FIG. 1. Servo data is written in the servo sectors 3 so as to produce a periodic output voltage shown in FIG. 2 when the magnetic head is moved in the radial direction of the magnetic disc 1. Referring to FIG. 2, the output voltage at 0 V corresponds to one of a plurality of concentric circles. Each concentric circle is called a track. About 30 servo sectors are required to properly access the magnetic head on the tracks. Moving the magnetic head from one track to another is called a "seek" operation.
In the case of performing a seek operation by the magnetic head, the conventional magnetic disc apparatus has the following drawback. Since servo data cannot be obtained in an area between two adjacent servo sectors (i.e., in a data sector), the output signal shown in FIG. 2 cannot be obtained when the magnetic head is aligned with a data sector.
Under these conditions, sampled signals are plotted in FIG. 2 for the velocities of the magnetic head, (i) 0.1 tracks/sector (indicated by circles), (ii) 0.5 track/sector (indicated by squares), and (iii) 1.5 tracks/sector (indicated by x). As may be apparent from FIG. 2, the position of the magnetic head can not be detected when the velocity exceeds 1 track/sector. Therefore, the magnetic head must be moved along the data sector at a velocity of one track/sector or less, thereby prolonging the seek time.